Spatial variability of Antarctic krill in relation to mesoscale hydrography

To examine the mesoscale distribution of Antarctic krill Euphausia superba Dana, length frequency and maturity stage data were subjected to multivariate analysis.The results showed that the population was heterogeneous with respect to size and maturity, with small immature krill found primarily inside the Bransfield Strait and large mature krill mainly north of the South Shetland Islands.Multivariate analysis of hydrographic data collected at the same stations revealed that the oceanography corresponded to previous classifications of the area, with Weddell Sea water in the southeast and east and South East Pacific water in the northwest.Further multivanate analysis using both krill variabhty and hydrographic data showed that a strong correlation existed between the krill distribution and the oceanography.Several hypotheses to explain the observed distribution of krill are dscussed.It is judged that neither simple processes, such as growth during the sampling period, nor processes whereby knll are advected passively through the area by water movement, can completely explain the observed distribution.Instead, it IS concluded that the observed gradient of krill size and matunty probably arises, at least in part, from an active ontogenetic migration.